From US-A 2009146543 plasma lamps are known. They are based on electrodeless high pressure discharge lamps which are often referred to as EHID. This citation is incorporated herein by reference.
Further References which deal with plasma lamps of this kind are:
Koch, B. (2002). Experimental examinations on new compact microwave resonators for electrodeless excitation of high-pressure discharge lamps. Light technical institute. Karlsruhe, University Karlsruhe; Dissertation [Experimentelle Untersuchungen an neuartigen kompakten Mikrowellenresonatoren zur elektrodenlosen Anregung von Hochdruckentladungslampen. Lichttechnisches Institut. Karlsruhe, Universität Karlsruhe; Dissertation.]
A device for plasma excitation by means of microwaves is disclosed as DE-A 103 35 523.
Details for Electrodeless HID Lamp with Microwave Power Coupler are published under CA-A 2 042 258 and CA-A 2 042 251.